In the field of packet communication systems typified by Internet communication and the field of mobile communication systems that transmit speech and audio signals, technology that transmits additional speech and audio information, text information, and/or image information such as that related to news at the same time as the speech and audio signals is desired.
Yet, simply multiplexing coded additional information with speech and audio signals coded by a coding apparatus using a relay apparatus (distributing apparatus) significantly increases the volume of information to be transmitted as well as communication costs and line usage rates, requiring a more innovative approach.
As prior art in this field, methods have been disclosed whereby a relay apparatus (distributing apparatus) at the time of speech signal transmission between mobile terminals decodes the speech and audio signals to be transmitted between the communication terminals, superimposes (combines) the decoded data on (with) additional information, codes the superimposed signals once again, and then transmits these coded signals to the other communication terminal (for example, Patent Document 1).
In recent years, scalable coding technologies have been developed that are capable of decoding speech and audio signals from just a portion of coded information to suppress sound quality deterioration even under conditions in which packet loss occurs (for example, Patent Document 2).
One representative example of this scalable coding technology is the method of repeatedly coding input signals in coding section of layer 1, obtaining that coded information, coding in the coding section of upper layer (where i is an integer greater than or equal to 2) the difference between the input signal of coding section of layer (i−1) and the decoded signal of the coded information of layer (i−1), i.e., the residual signal, as the input signal of layer i, and obtaining the coded information.    Patent Document 1: Japanese Patent Application Laid-Open No. 2003-304336    Patent Document 2: Japanese Patent Application Laid-Open No. H10-97295